If you think about it the metal toothed cups used in harmonic drives, have to flex in a rather nasty way (it is a little more than just squeezing the mouth into an oval). I'm surprised they last as long as they do. I'm not surprised you are having cracking problems with the pla. What is the distance from where the cup is pinched by the bearing to the face of the cup? Increasing that distance should improve the durability. Also I think I would slightly increase the thickness and add a slight fillet to the inside transitioning from the wall to the cup face. Then taper the cup wall down and have it be it's thinnest (probably thinner than you have it now) for the majority of the height of the cup then thicken it again to accommodate the toothed surface at the bottom.
I do have the remains of a busted commercially made harmonic drive in a box on a shelf. It was in the tool changer of a used machine we bought. I don't know how it was originally broken, but it to failed at the transition of wall to face, the previous owner had tried to fix it by welding the cup back together. It worked for about 6 months after we bought the machine, until the welds fatigued and failed. In the mean time the part was redesigned by the harmonic drive manufacturer with a much taller cup for the replacement part (also requiring us to replace of a number of other parts in our tool changer to accommodate the redesigned part.) Todd Zuercher P. Graham Dunn Inc. 630 Henry Street Dalton, Ohio 44618 Phone: (330)828-2105ext. 2031 -----Original Message----- From: Gene Heskett <[email protected]> Sent: Friday, August 28, 2020 11:10 AM To: [email protected] Subject: SPAM: Re: [Emc-users] precisiomn indexer [EXTERNAL EMAIL] Be sure links are safe. On Friday 28 August 2020 06:18:32 Thomas J Powderly wrote: > Gene an old client called about using a Newbould indexer on his > machine. > > I remember it was a hirth 'gear' or coupler > > Very accurate stacking 'gears' , a way to set a part at precise angles > > I thought... "Hey Gene could _print_ one" > > as if you dont have enough to do :-) > > just FYI > > TomP > > https://en.wikipedia.org/wiki/Hirth_joint > > https://www.youtube.com/watch?v=3EGGuR5YziE > The odd tooth version could probably be done in sub-degree jumps but not with a 3d printers tolerances. I'm learning how to make flexgears for a harmonic drive out of TPU. PLA hasn't enough flex and breaks in less than 5 minutes running time. And I've two that have now run at an output speed of about 1 rev in 4 seconds for over 24 hours. Unlike the really preciely made metal one's, it has to have a touch of backlash, but with a decent driver, and none of the TB series fit that description, because they don't auto-throttle the currants, it looks like I'll have enough torque from a nema 17 motor to drive the worm of a clone BS-1, under cutting load no less. TPU can be a cast iron bitch, its 100x more finicky about temps and speeds than PLA. Currently seems to be working, but at a nozzle temp 15C above whats noted on the no-name box I bought 2 of for a $70 bill. Virtually zero extruder drive grip allowed in a Micro-Swiss hot end that moves the extruder motor to the X carriage. Thanks TomP, stay safe and well, both of you. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
